1. Field of the Invention
The present invention relates to an optical recording method in which an image is recorded on, for example, a plate for lithography or lithoprinting by directly irradiating the plate with high-power laser light, and also relates to an optical recording apparatus, an optical recording system and an optical recording medium to be used for conducting such an optical recording method.
2. Description of a Related Art
With a CTP (Computer to Plate) or CTC (Computer to Cylinder) plate making system in the field of printing, a plate is fabricated in such a way that image information accumulated in a computer is recorded on a photosensitive plate material (sensitized material) by using a laser scanner or the like, and that the recorded image is developed. According to the system, intermediate printing films for respective colors in a conventional photoengraving process are dispensed with. Therefore, the system is in the limelight as one having the advantages of cost curtailment, rapid processing, quality enhancement, etc.
In that depiction of the CTP or CTC plate making system which employs laser light on the basis of light-to-heat conversion, the sensitivity of the sensitized material is low to lower a depicting speed, and hence, the light of high power needs to be used for the recording. Therefore, the sensitized material has been chiefly submitted to parallel depiction by using a sensitized material mounting/recording system of outer drum type in which a plate with the sensitized material deposited on a base material backing is wound outside a drum, and by employing a laser array which includes several tens semiconductor lasers of watt class.
Such a recording system utilizing the light-to-heat conversion, however, has had the disadvantage that, since heat radiates to an ambient medium, lowering in an effective recording sensitivity is oftener incurred due to thermal diffusion as the recording is done more slowly by the parallel depiction. This phenomenon is called the xe2x80x9clow illuminance failurexe2x80x9d, and is detailed in Hare et al. xe2x80x9cNew Method for Exposure Threshold Measurement of Laser Thermal Imaging Materialsxe2x80x9d, Journal of Imaging Science and Technology Vol. 41, No. 6, November/December 1997, p588-593. Especially in case of employing aluminum which is common as a material of the base material backing, the thermal diffusion is heavy, so that the recording sensitivity has lowered conspicuously. Another evil effect has been that the recorded image is obscured by the thermal diffusion.
With the intention of improving the drawbacks, Japanese Patent Application Laid-open JP-A-10-146996 discloses a method wherein the effective recording sensitivity is raised by heightening the scanning speed of a laser beam.
Besides, Japanese Patent Application Laid-open JP-A-11-254741 discloses a method wherein the shape of a laser beam on the sensitized material is narrowed in a main scanning direction into a flat shape, thereby to shorten the projection time of the laser beam at each point on the surface of the sensitized material and to raise the effective recording sensitivity.
Meanwhile, the sensitized material has also been submitted to the depiction by using a sensitized material mounting/recording system of inner drum type in which the plate with the sensitized material deposited on a base material backing is wound inside a drum, and by employing a YAG (Yttrium Aluminum Garnet) laser which continuously oscillates at a high power of about 10 watts or above. In this case, an image is recorded by combining an external modulator such as AOM (Acousto-Optic Modulator), and the scanning of a laser beam based on a high-speed rotating mirror. According to such a sensitized material mounting/recording system of the inner drum type, the effective recording sensitivity can be raised by shortening the projection time of the laser beam at each point on the surface of the sensitized material. However, the rise of the sensitivity is an effect derived from the necessity of recording the image at high speed by employing the single light source, and still more rise in the sensitivity has not been realized.
Therefore, further rise in the recording sensitivity is desired even when the techniques of the improvements in the sensitized material mounting/recording systems of the inner drum type and the outer drum type as explained above are employed.
The present invention has been made in view of such problems. A first object of the present invention is to raise an effective recording sensitivity in the recording of image information on a photosensitive material, whereby a productivity is enhanced owing to lowered energy (laser power) necessary for the recording or a heightened recording speed. Besides, a second object of the present invention is to improve the evil effect that a recorded image is obscured due to thermal diffusion, whereby the sharpness of the recorded image is enhanced.
In order to accomplish the objects, an optical recording method according to the present invention, wherein an image is recorded by projecting a light beam onto a photosensitive material formed on a base material backing, comprises the steps of: (a) successively outputting pulse light having a duty factor of at most 50%, from a light source; (b) modulating the pulse light output from the light source, in accordance with an image signal, and then projecting the modulated pulse light onto the photosensitive material; and (c) recording the image by causing the pulse light to scan the photosensitive material.
Besides, an optical recording apparatus according to the present invention, wherein an image is recorded by projecting a light beam onto a photosensitive material formed on a base material backing, comprises: a light source for successively outputting pulse light having a duty factor of at most 50%; modulation means for modulating the pulse light output from the light source, in accordance with an image signal, and then projecting the modulated pulse light onto the photosensitive material; and scanning means for causing the pulse light to scan the photosensitive material, thereby to record the image.
Further, an optical recording system according to the present invention comprising: an optical recording medium including a photosensitive layer formed on a base material backing, the photosensitive layer including a photosensitive material for recording an image when a light beam is projected thereon and having a thickness of at most 15 nm; a light source for successively outputting pulse light having a duty factor of at most 50%; modulation means for modulating the pulse light output from the light source, in accordance with an image signal, and then projecting the modulated pulse light onto the photosensitive layer; and scanning means for causing the pulse light to scan the photosensitive layer, thereby to record the image.
In addition, an optical recording medium according to the present invention comprising: a base material backing; and a photosensitive layer formed on the base material backing, the photosensitive layer including a photosensitive material for recording an image when a light beam is projected thereon and having a thickness of at most 15 nm.
According to the present invention constructed as described above, an image is recorded using pulse light having a duty factor of 50% or below, whereby an effective recording sensitivity in optical recording can be enhanced. It is accordingly permitted to lower total energy necessary for the recording or to enhance the productivity by heightening a recording speed. Further, the energy for the recording is lowered, whereby the obscurity of the recorded image attributed to thermal diffusion can be improved to enhance the sharpness thereof.